The present invention relates to a plasma display panel technology; and, more particularly, to an energy recovery unit of a sustain driver in an AC-type plasma display panel.
A plasma display panel(PDP) is a device for displaying a picture and it has been known as a gas discharge display device. Discharge gases, such as Kr and Xe, are filled up between upper and lower panels of the plasma display panel, and an ultraviolet ray generated through the gas discharge exciting red, green and yellow fluorescents, which are formed at least one of the upper and lower panels thereby to generate visible lights.
The PDP is classified into a DC type and an AC type. In the DC type PDP, electrodes for applying voltage to the panel is exposed directly to the discharge gas so that a current directly flows between electrodes in order to form the plasma. Therefore, it is advantageous that the structure is relatively simple. On the other hand, it has disadvantage that the external resistor has to be placed to limit the current. In the AC type PDP, the electrodes are covered with the dielectric substances so that the electrodes are not exposed directly to the discharge gas in order to flow a displacement current. The AC type PDP has longer life span, compared with the DC type PDP, because the electrodes of the AC type PDP can be protected from an ion impact by covering the electrodes with the dielectric substances to limit the current naturally. The AC type PDP can be classified into an opposite discharge type and a surface discharge type. The opposite discharge type has the disadvantage that the life span is shortened by the degradation of the fluorescent substances owing to the ion impact. In the surface discharge type, on the other hand, the discharge is generated near the front panel opposite to the fluorescent substances in order to minimize the degradation of the fluorescent substances, therefore, the surface discharge type is adopted to most of the PDP manufacturing processes.
In the AC type PDP, the high voltage has to be applied continuously and alternately between the sustain electrodes (X electrode and Y electrode) in the discharge cell during the operation of the PDP. Therefore, the dielectric substances are spread over the sustain electrodes so that a panel capacitor exists between X electrode and Y electrode.
In order to alternatively apply the positive and negative high voltage between the sustain electrodes during the operation of the PDP, the charge and discharge operations of the panel capacitor has to be performed. However, the power is consumed considerably by the panel capacitor during the charge and discharge operations, and the power loss problem of a panel drive circuit is generated because the capacitance of the panel capacitor is increased in proportion to the size of the panel.
In order to solve the power loss problems in the panel drive circuit, an energy recovery unit is adopted to the conventional panel drive circuit. In the energy recovery unit, an inductor for forming a LC resonance circuit with the panel capacitor is used to recover the energy loss during the discharge of the panel capacitor. The energy is stored in the inductor through the recovery, and the stored energy is used during the next charge operation of the panel capacitor to reduce the power loss.
A conventional circuit structure of a Weber-type sustain driver in the PDP having an energy recovery unit is shown in FIG. 1.
Referring to FIG. 1, a sustain driver, in the PDP having the energy recovery unit, includes a first and second sustain drivers 100 and 200 which are connected across a panel capacitor Cp.
The first sustain driver 100 includes a driving unit 12 and an energy recovery unit 10. The driving unit 12 drives the panel capacitor Cp to a sustain voltage Vsus or the ground voltage. The energy recovery unit 10 recoveries the energy loss caused during the discharge operation of the panel capacitor Cp and provides the recovered energy to the panel capacitor Cp during the next charge operation.
The first and second sustain drivers 100 and 200 have symmetrical configuration across the panel capacitor Cp. During the charge and discharge operations, the voltage Vp of the panel capacitor Cp is swung to positive and negative voltage by the first and second sustain drivers 100 and 200 operating alternatively with each other. Therefore, the detailed diagram of the second sustain driver 200 is not shown in FIG. 1, because the second sustain driver 200 has the same structure with the first sustain driver 100.
The driving unit 12 of the first sustain driver 100 includes a first switch S1 and a second switch S2. The first switch is connected to a power source supplying the sustain voltage Vsus and the panel capacitor Cp and transfers the sustain voltage to the panel capacitor. The second switch S2 is connected the ground and the panel capacitor Cp and transfers the ground voltage to the panel capacitor.
The first energy recovery unit 10 in the first sustain driver 100 includes an inductor Lr, an external capacitor Ce, third and fourth switches S3 and S4, and first and second diodes D1 and D2.
The inductor Lr is connected to the panel capacitor Cp for operating the panel capacitor Cp with a half resonance. The external Capacitor Ce stores the energy recovered by the resonance operation of the inductor Lr and the panel capacitor Cp. The third and fourth switches S3 and S4, coupling in parallel, are connected to the external capacitor Ce for switching an energy recovery path. The first and second diodes D1 and D2, coupled in parallel and to reversal direction with each other, are respectively connected to the third and fourth switches S3 and S4. The inductor Lr is connected to the first and second diodes D1 and D2 in order to prevent a reverse of resonance current IL.
Each switch S1, S2, S3 and S4 can be formed with a metal oxide semiconductor field effect transistor (MOSFET), a reversal and parallel connected diode or an insulate gate bipolar transistor (IGBT).
A resonance frequency (f0) of a L-C series resonance circuit can be described as formula 1:
f0=xc2xd (LC)1/2.xe2x80x83xe2x80x83[Formula 1]
A resonance cycle (T) can be described as formula 2:
T=2 (LC)1/2.xe2x80x83xe2x80x83[Formula 2]
A resonance current has a period of 2 (LC)1/2, and the maximum resonance current is generated in a condition of a half resonance, xcfx80 (LC)1/2.
FIG. 2 shows waveforms of the sustain driver having the energy recovery unit shown in FIG. 1. In FIG. 2, a waveform of the voltage Vp of the panel capacitor Cp, a waveform of the resonance current IL, and each waveform Vg(S1), Vg(S2), Vg(S3) and Vg(S4) of switch S1, S2, S3 and S4, are shown.
Referring to FIG. 2, the first sustain driver 100 is operated by setting four periods T1 to T4 as one cycle. The energy of Vsus/2, recovered from the panel capacitor Cp in the previous cycle, is stored in the external capacitor Ce of the first energy recovery unit 10.
An initial condition reflects the operation of the second sustain driver 200. In the period of T0, the second switch S2 in the driving unit 12 of the first sustain driver 100 is turned on and a pull-down switch (not shown) in a driving unit of the second sustain driver 200 is turned on to form a closed-loop. At this time, the voltage Vp of the panel capacitor Cp is the ground voltage 0V and the resonance current IL does not flows.
In the first period of T1, a current path is formed between the external capacitor Ce and the panel capacitor Cp by turning on the switch S3. At this time, the resonance current IL is formed by the resonance operation of the inductor Lr and the panel capacitor Cp so that the voltage Vp of the panel capacitor Cp increases up to the sustain voltage Vsus.
In the second period of T2, the voltage Vp of the panel capacitor Cp is sustained to the sustain voltage Vsus by turning on the switch S1. The switch S3, however, should be turned on until a xc2xd resonance cycle is completed, and the switch 3 can be either turned on or turned off after the xc2xd resonance cycle.
In the third period of T3, the current path is formed between the panel capacitor Cp and the external capacitor Ce by turning off the switch S1 and turning on the switch S2. The energy stored in the panel capacitor Cp by the resonance operation of the inductor Lr and the panel capacitor Cp is recovered to the external capacitor Ce.
In the fourth period of T4, the voltage Vp of the panel capacitor Cp is sustained to the ground voltage 0V by turning on the switch S2. The switch S4, however, should be turned on until a xc2xd resonance cycle is completed, and the switch 4 can be either turned on or turned after the xc2xd resonance cycle. Further, a closed-loop is formed by turning on the pull-down switch (not shown) of the driving unit in the second sustain driver 200 during the operation of four periods T1 to T4 in the first sustain driver 100.
Thereafter, the operations of four periods, T1 to T4, are performed in the second sustain driver 200. At this time, the voltage Vp of the panel capacitor Cp becomes the negative voltage.
The power loss can be reduced by the conventional PDP comprising the energy recovery unit, that is, the energy stored in the external capacitor Ce, and the panel capacitor Cp is charged and discharged with xc2xd resonance of the inductor IL and the panel capacitor Cp in the sustain drivers.
In addition, the voltage Vp of the panel capacitor increases to the sustain voltage Vsus by the resonance current IL and the current transferred from the external capacitor Ce charged with Vsus/2 during the first period of T1. However, actually, a voltage drop xcex94, i.e. an energy loss, is generated by a resistance of connection lines and by parasite resistances of devices in the PDP for the charging and discharging operations. Therefore, the efficiency of the energy recovery and the driving characteristic of the PDP are degraded.
It is, therefore, an object of the present invention to provide an energy recovery unit of sustain driver in AC-type plasma display panel (PDP) capable of preventing lowering of an energy recovery efficiency owing to the parasite resistance and improving a drive characteristic of the PDP.
In accordance with an aspect of the present invention, there is provided a plasma display panel (PDP) comprising: a panel capacitor representing panels of the PDP; a driving unit for driving the panel capacitor to a sustain voltage and ground voltage; and an energy recovery unit for recovering and supplying energy together with the driving unit, wherein the energy recovery unit includes, a first inductor for forming a xc2xc cycle resonance unit with the panel capacitor when the panel capacitor is charged; a second inductor for forming a xc2xc cycle resonance unit with the panel capacitor when the panel capacitor is discharged; and an external capacitor for supplying an energy to the xc2xc cycle resonance unit and storing recovered energy.
In accordance with another aspect of the present invention, there is provided a A plasma display panel (PDP) comprising: a panel capacitor representing panels of the PDP; a driving unit for driving the panel capacitor to a sustain voltage and ground voltage; and an energy recovery unit for recovering and supplying energy together with the driving unit, wherein the energy recovery unit includes, a first inductor for forming a xc2xc cycle resonance unit with the panel capacitor when the panel capacitor is charged; a second inductor for forming a xc2xc cycle resonance unit with the panel capacitor when the panel capacitor is discharged; and an external capacitor, of which voltage level is the sustain voltage, for supplying an energy to the xc2xc cycle resonance unit and storing recovered energy.
In the present invention, a panel capacitor is charged and discharged with xc2xc resonance of the panel capacitor and an inductor in an energy recovery unit, and the energy is stored in an external capacitor. Therefore, the charge and discharge operations of the panel capacitor can be carried out, sufficiently, regardless of an amount of a parasite loss, and the effect of a panel discharge generated during a recovery period can be reduced. For achieving the above-mentioned advantage, the energy recovery unit of the present invention further comprises a first inductor and a second inductor. The first inductor generates xc2xc resonance with the panel capacitor in case of charging the panel capacitor, and the second inductor generates xc2xc resonance with the panel capacitor in case of discharging the panel capacitor and external capacitor. In charge and discharge periods of a panel capacitor, a voltage Vsus is provided to a LC serial resonance circuit, which is comprised of the panel capacitor and two inductors, thereby to recover remnant energy.